SO my serpentine tensioner started knocking back and forth when my ac is on and my car is at temp after driving for a while. Only when i run the ac at idle, after it knocks a few times it shuts the ac clutch off.
Seemed to start when i added a can of coolant to it to get the ac a little colder. Could i of over pressured it? What should it be at? I used a cheepo gauge and it was in the bottem of the green when i was done haha.

I was going to order a new tensioner but got to thinking that maybe its the ac clutch slowing the belt down putting the extra stress on the tensioner because of to much pressure.

 

It's knocking back and forth because the bearing inside your AC pulley is about to say goodbye and then it will snap you belt.thats what happened to me.buy short rout(AC bypass) belt so you can change it on the road if that happens.

 

It was too much pressure in the ac system, i removed some and now it works grate again with no noise. Not sure why i made a thread when i was almost sure i knew what it was.